Spencer on water vapor feedback

I wonder if we could get Dr. Spencer to comment on the latent heat effect of the water cycle. As water evaporates from the surface, it carries latent heat with it, cooling the surface. Convective transport of this water vapor to higher altitudes effectively moves that energy around the greenhouse effect. When that vapor condenses, it not only removes the vapor, but emits that stored latent heat at a higher altitude, bypassing much of the greenhouse effect. If higher temperatures drive more evaporation and precipitation, then they also drive greater convective transport of latent heat. At least, that’s what appears to me.

Rows and floes of angel hair
And ice cream castles in the air
And feather canyons everywhere
I’ve looked at clouds that way
But now they only block the sun
They rain and they snow on everyone
So many things I would have done
But clouds got in my way
I’ve looked at clouds from both sides now
From up and down, and still somehow
It’s cloud illusions I recall
I really don’t know clouds at all

What John Galt said. Also more clouds leads to more sunlight being reflected straight back out into space.

Neil – It failed it a long time ago. It’s one of the big problems with climate models. I’m not sure how they’ve addressed it. Lindzen would talk about this frequently.

“I will admit to having waffled on this issue over the years, but that’s because there is evidence on both sides of the debate.”
You and everyone else, Roy. This is the key issue yet we seem no nearer to solving it than we were ten years ago. Meanwhile huge sums are being wasted on yet more anecdotal observation to support a meme based on a few tenths of a degree rise in temperature (cause unknown) over a period of time that gets ever shorter as the odd wheel falls off. And the economic hinterland behind it grows more massive by the day.
This to me defines “Climate Science” – the business of reinforcing anecdotal evidence to support conjecture, supposition and an agenda while avoiding pursuit of the truth.
Surely it is not that difficult to roll out a programme to sort this issue out based on sound empirical evidence. In a rational world, is that not what the IPCC and all the rest ought to be doing? How much would it cost to improve water vapour measurements from the radiosondes you mention compared to launching yet more satellites to confirm water freezes and thaws seasonally by varying amounts? If you want to play with satellites how about a matrix of them to replace the aging ERBE and measure the earth’s radiation budget directly and accurately over the entire globe? The key question is why this hasn’t already been done as a matter of urgency.
Why, when it’s supposedly the survival of the human race that’s at stake? Hang the cost. There’s only so much spleen grease and post normal clap trap one can swallow before the obvious kicks in I’m afraid, no need for conspiracy theories.

More moisture in the air, more clouds, rain, storms, which seek to remove the latent head and ensure stability. If these systems didnt exit, the earths atmosphere would have gone nuts a long time ago. Its no coincidence that the moonson permanently sits over the area of the earth recieiving the most energy.
You cant have more evaporation, cloud cover and rainfall whilst also having more warmth, it just doesnt work!

As I have stated earlier, I personally suspect that role played by earthshine emitting/absorbing (greenhouse) gases at the tropopause level may be being underestimated as a mechanism for removing convected heat from the atmosphere. I would think that the most important spectra may be those lines that have a 50 percent chance of getting out from that level at the typical temperature of 220 K as I believe these should have the highest relative emissivity.
The important parameter for measuring how effective convection is as a thermal regulator of surface temperatures would be a determination of how the effective surface temperature, as controlled by the adiabatic lapse rate from the tropopause temperature, would change as a function of the total energy being convected upward. This would account both for tropopause altitude changes and temperature changes with increasing upward convected thermal energy. I do not know if anyone has ever attempted to estimate or determine this.

I posted this comment at Roy Spencer’s blog, still in moderation:
——–comment——

At a minimum, I believe the water vapor feedback issue is more complicated than most mainstream researchers think it is..

I think it’s very complicated and I can’t comment on “most researchers” whereas you would probably know a lot of them – plus their papers may well be more cautious than their general views.
But the papers I’ve read don’t appear to deal with it simplistically and do cover these same questions. Of course some of the papers I’ve read are “Spencer & Braswell 1997″, Lindzen, but also Soden & Held, Sun & Oort, Bony & Duvel, Ramanathan, many others.
In Clouds and Water Vapor Part Two I cited Held and Soden (2000):

To model the relative humidity distribution and its response to global warming one requires a model of the atmospheric circulation. The complexity of the circulation makes it difficult to provide compelling intuitive arguments for how the relative humidity will change. As discussed below, computer models that attempt to capture some of this complexity predict that the relative humidity distribution is largely insensitive to changes in climate.

Held and Soden have their point of view but in theirs and most of the papers I don’t see a simplistic approach.
—end of comment—
Water vapor feedback is a complex subject. You can see the approach of the great Ramanathan in Clouds and Water Vapor – Part One. For those who don’t simplistic answers, it’s worth taking a look. Many interesting comments as well.

Dr . Spencer is asking the most important question of all and thinking about the possible answers(s). He, and others asking similar questions, know that the “science is (not) settled”. With an open mind, we look forward to further work in this crucial area!

Ferenc M. Miskolczi’s paper Greenhouse Effect in Semi-Transparent Planetary Atmospheres published in the Quarterly Journal of the Hungarian Meteorological Service in 2007 explores the effects of humidity.
http://met.hu/doc/idojaras/vol111001_01.pdf
“Abstract—In this work the theoretical relationship between the clear-sky outgoing infrared radiation and the surface upward radiative flux is explored by using a realistic finite semi-transparent atmospheric model. We show that the fundamental relationship between the optical depth and source function contains real boundary condition
parameters. We also show that the radiative equilibrium is controlled by a special atmospheric transfer function and requires the continuity of the temperature at the ground surface. The long standing misinterpretation of the classic semi-infinite Eddington solution has been resolved. Compared to the semi-infinite model the finite
semi-transparent model predicts much smaller ground surface temperature and a larger surface air temperature. The new equation proves that the classic solution significantly overestimates the sensitivity of greenhouse forcing to optical depth perturbations. In
Earth-type atmospheres sustained planetary greenhouse effect with a stable ground surface temperature can only exist at a particular planetary average flux optical depth of 1.841 . Simulation results show that the Earth maintains a controlled greenhouse effect with a global average optical depth kept close to this critical value. The broadband
radiative transfer in the clear Martian atmosphere follows different principle resulting in different analytical relationships among the fluxes. Applying the virial theorem to the radiative balance equation we present a coherent picture of the planetary greenhouse effect.”
SPPI published a paper last December by another Hungarian scientist, Miklos Zagoni, discussing Miskolczi’s work, which was based on actual observations and measurements. You might recall that Miskolzci was a senior scientist at NASA, which refused to publish his work. The SPPI paper can be found here –
http://scienceandpublicpolicy.org/originals/co2_cannnot_cause.html?Itemid=0

Ceri Phipps says:

Water vapour can not be a positive feedback as there is no limit to available water and consequently if it were a positive feedback the atmosphere would be saturated with respect to water vapour which it is not..
The idea that water vapour can be a positive feedback makes no scientific sense. It is blatantly obvious that there is a large negative feedback that keeps it in balance. Clouds and rain seem the most obvious.

It doesn’t make intuitive sense for those used to thinking about control systems – positive feedback usually leads to some kind of runaway system.
However, in the case of the climate there are also some non-linear negative feedbacks – surface radiation increases in proportion to the forth power of (absolute) temperature. If you analyze the system mathematically, a higher range of potential positive feedback leads to a thermal runaway. The lower range of positive feedback leads to amplified warming (compared with no feedback), and of course, negative feedback leads to reduced warming.
This doesn’t mean that water feedback is a positive feedback. But the idea isn’t mathematical or scientific madness.

“Warmer air is associated with greater surface evaporation rates….”
Yes, but other effects have such as wind speed have large impacts on evaporation rate. Wind can dry the surface (that is evaporate water) on cold days/nights quicker than warmer days/nights with no wind. The GHG IR effect is of little relevance where wind dominates.
Spector says:
“As I have stated earlier, I personally suspect that role played by earthshine emitting/absorbing (greenhouse) gases at the tropopause level may be being underestimated as a mechanism for removing convected heat from the atmosphere. ”
This is something that is not often referred to, as the energy transfer diagrams never seem to include the effect of IR active gases on the absorption/re-radiation of IR receivedfrom the sun. Nor do they really consider what happens at night, when GHG’s are for the most part atmospheric coolers.

We don’t know if water vpour is increasing as predicted.
We don’t know if increased water vapour is producing or will produce a net warming as predicted.
Since it is expected to be responsible for close to 2.0C of the warming by 2100, it is a little strange that we still don’t have any evidence to say one way or the other.

From scienceofdoom:
“In fact, even the best known one, by Kiehl and Trenberth shows 1/3 of the solar radiation being absorbed by the atmosphere.
At night? Well, I don’t know what diagrams you are referring to, but in the case of Kiehl and Trenberth for example, this is a globally, annually averaged diagram, so you won’t see day and night. But once again, this is climate basics so it is considered in every climate model.”
My take on this: The K&T diagram shows the 1/3 absorption, but does not say in which energy bands it takes place. If it is shorter wavelength, there is no GHG/IR re-radiation. It does show emitted radiation, but the diagram implies that the source of this radiation is from the surface/clouds, not the re-radiation of the incoming energy in the upper atmosphere.
The day/night effects are lumped together, but it would be instructive to see them separated so that the compensating IR heating/cooling effects can be clearly shown.
As a style criticicism, the K&T diagram also attempts two analyses on the same image. Namely, on the left there is an energy analysis in direct W/m2. On the right it also uses W/m2, but as part of a black body cloud/surface interchange, with the apparently anomalously large numbers actually being correctly expressed artefcats of the blackbody dynamics.

As per usual I’m prolly missing something, but water vapor isn’t a coolant.
Water is a coolant, just try it in a desert, or hell spill your water on your crappy ski pants high up in the mountains at minus 20 but I guess a big commercial freezer works too. When in the jungle in the summer time everyone present want those instant 15 minute showers, cool things down a bit… however afterwards it get warmer due to the water vapor raising from the ground, cloths drying, and what not. In the desert it really is the same you just doesn’t really notice the difference when the splash in the face that cooled things down for a micro second is then vapor in the atmosphere, the vaporization process is felt as cooling though.

IMO Cohenite hits the nail on the head. As an engineer I have studied feedback systems and positive feedback results in system failure. We know this for a fact. If CO2/H2O forcing was positive we would have become Venus a long time ago when CO2 levels were many times what they are now. How can scientists continue to say “we have no real ideal how water vapor, by far the strongest greenhouse gas, responds to increasing temperatures but we’re pretty sure it’s catastrophic” despite the evidence all around them. At what point do reasonable people call bullcrap?

jorgekafkazar said on Spencer on water vapor feedback
September 15, 2010 at 10:03 am
Yes, clouds do absorb CO2. Relatively pure rain will have a pH that is roughly in equilibrium with the atmospheric concentration (between 5 and 5.5). Some CO2 will be returned to the ocean surface in rain. Some will be transported up in towering clouds where the water freezes and releases CO2 to the upper atmosphere. This process of evaporation/condensation/freezing will occur many times as an air mass containing clouds goes from the equator to the poles. http://www.kidswincom.net/climate.pdf.

How do any of us negative feedback ourselves when too hot? With water. Water refreshes. Do some alien “peers” think differently? Probably,…. if cold-blooded.

In the past, various posts here at WUWT have hit on the issue of water vapor needing microscopic “particles” to latch on to in order to form precipatation. From what I’ve seen, there’s more than enough microscopic particles in the atmosphere (man-made and not) to rain and snow on everyone for 400 days and nights. Has the “dramatic” (my opinion) increase in smog+ in the last 50 years, at various levels of altitude, been studied vis-a-vis humidity and rainfall? Do they plug this info into climate models at NOAA and The Met Office?

Pascvaks says:
September 15, 2010 at 12:34 pm
The visible part of smog is made up of sub-micron sulfuric acid aerosols. Their size is a function of relative humidity and are usually at their smallest during the hottest time of day. Like clouds, they reflect, absorb, and radiate different levels of energy. Some have proposed injecting this harmful pollutant into the upper atmosphere to reflect incoming energy from the sun back to space. To me that is poison pie in the sky.

Hi Roy. Reading this something twigged in my memory and the following thought occurred:
You know those atmospheric heat distribution graphs that show a general heating over the past 3 decades near the surface of the earth but fail to show the tropical hot spot predicted by the GCMs? The same graphs show high altitude cooling during the same period.
Taking the graphs at face value, what we’ve got is an atmosphere that is, on the whole, warmer than it used to be near the surface, and COLDER than it used to be up in the stratosphere.
Combine an increasingly steeper temperature gradient with the proposed increasing H2O vapour and you get … ice crystals at higher altitudes (do you not?). And high-altitude ice constitutes a strong negative feedback by its effect on albedo (does it not?).
It would seem this consideration is easy to model, intuitively pretty obvious, and the corresponding physics is well enough known to lend itself to back-of-the-envelope calculations concerning feedback. What would these suggest?

Gerry says on September 15, 2010 at 4:48 pm

Dr. Spencer,
This is rarely accepted well even at WUWT, but a fundamental tenent of engineering is that unstable systems do not long survive. Systems dominated by positive feedbacks are not stable by definition. That the earth’s climate is bounded within a narrow range over long geologic time demonstrates beyond doubt that it is a system dominated by negative feedback.
And yet the earth’s climate as dominated by positive feedbacks is routinely debated within the climate community as if it can be a possibility.
All of engineering await the climate scientist who can re-write this basic control theory component.

Gerry, is it even possible to be a little bit pregnant?
That is, is it even possible to be stable over the long term with a small amount of positive feedback?

Richard;
Try getting just a little speaker howl feedback by positioning the mic just so. Can’t be done. The rise time to the howl is almost entirely a function of the speed of transmission between the two points.

Ceri Phipps says:

If the atmosphere warms, the amount of water vapour it can hold increases, therefore if there were a positive feedback it would not matter what caused the warming, it would kick of a positive feedback until the atmosphere became saturated with water vapour. This should, therefore, have happened in the last El Nino event, which it clearly didn’t.

You might want to look up Xeno’s Paradox. An infinite sum does not have to diverge to infinity. For example, if each 1 deg rise in temperature causes additional water vapor to go into the atmosphere that results in 1/2 deg rise in temperature then this 1/2 deg rise in temperature will cause additional water vapor to go into the atmosphere to produce an additional 1/4 deg rise. What you get is a sum like 1 + 1/2 + 1/4 + 1/8 + 1/16 + …, which converges to the value of 2, thus doubling the original temperature change in the absence of the water vapor feedback.
Reply: Xeno’s paradox also applies to roommates who don’t want to appear to finish off the food in the refrigerator thus converging to zero food in the container while never quite reaching it. ~ ctm

“”” Joel Shore says:
September 15, 2010 at 6:21 pm
Gerry says:
This is rarely accepted well even at WUWT, but a fundamental tenent of engineering is that unstable systems do not long survive. Systems dominated by positive feedbacks are not stable by definition.
…
All of engineering await the climate scientist who can re-write this basic control theory component.
It is not a re-write of control theory. It is, however, a different usage of the term when climate scientists talk about a “net positive feedback”. “””
Well Gerry is not really correct either. Positive feedback is NOT automatically unstable. And positive feedback is used quite routinely in lots of engineereing situations.
For a start; positive feedback was very popular in a lot of early radio receivers; where it was used to increase the circuit gain of many radiao receivers. But the use of positive feedback does increase the noisiness of systems and since early radio receivers were quite noisy anyway; if you got too close to the edge with your positive feedback, then the general noisiness could throw you into an oscillatory state.
Positive feedback was very common in automobile drum brakes; where a “Two leading shoe” architecture was used to reduce brake pedal pressures. In a two leading shoe design, the brake shoes are pivoted at the “front end” in terms of the normal direction of rotation, and (of course) at a smaller radius than the brake surface. When the brakes are applied, the friction drags the brake shoe in the forward direction and that causes the shoe to try and pivot outwards in radius; thus increasing the force against the brake drum; which further increased the friction; and the pivoting moment. Although this reduced the brake pedal force it also increased brake fade. Whent eh shoes get too hot; boning materials in the brake linings tend to melt and flow out onto the shoe surface making it kind of glassy, and dropping the coefficient of friction. When the coefficient of friction dropped thus causing the brakes to fade, it also dropped the positive shoe wrtapping feedback so the fade got even worse.
The simplest drum brakes; had a single fixed pivot point for both shoes and a single brake cyclinder pushing the opposite ends apart; which was cheaper; one cylinder (and less unsprung weight). So this system has one leading show and one trailing shoe. The leading shoe self wraps giving positive feedback; while the trailing shoe tends to unwrap; which is negative feedback. This is more stable against fade; but needs more pedal pressure. Also the leading shoe does more work than the trailing shoe so you need either thicker brake lining on the leading shoe or they will wear out at different times.
Once air and hydraulic assist came along; the fancier automobiles went to two traing shoe brakes which had only negative feedback; but needed the pedal boost. If the shoes got hot and the coefficient of friction dropped, the unwrapping effect also dropped raising the force on the shoe; so they were much more stable against brake fade.
Of course disk brakes got rid of all of those problems.
Positive feedback is only unstable if the loop gain exceeds unity; well the exact definition of unstable based on a pole zero plot and the like; is a bit more pedantically correct; but the end result becomes a greater than unity loop gain.
As to your S-B negative feedback Joel, it is also highly non-linear feedback; whcih makes it all the more powerful a controlling effect. Of course the control (in terms of increasing Temperature and radiation) is rather what we don’t want too much of.
But there are more negative feedbacks besides the S-B, such as the H2O interception of signigficant amounts of incoming solar energy; by H2O vapor which is then down converted to LWIR but half of that escapes, and only half reaches the surface; so there is anet loss of solar energy to the surface; so it is a negative feedback (but the H2O vapor is also having posivie feedback by direct interception of LWIR fromt eh surface; same as CO2 does.
But then there is the overflow clamp of cloud formation which simply stops any positive feedback loops in their tracks; and only H2O does that.

Roy Spencer, real scientist. Thankyou for that posting. I agree with Gerry , stability, with a tendency to iciness, is apparent in the geological record, apparently volcanic eruptions have increased atmospheric co2 abruptly in the past, but no run away warming. No control technology will remain operational under the assumptions of AWG theory but its still considered a valid theory? It takes a genuine scientist to attempt to explain what we know we do not know and why climate science is still very young and maybe not yet a science. Recently I have been wondering what of the sweeping claims of global warming science remain? Most of the alarming ,worse than ever ,claims were DOA and I’ve lost track. I read the IPCC 4th report and it did not support the claims made in its name.

I sort of get it:
The more you heat or cool the Earth, the more or less precipitation will carry the warmer water vapor aloft, where the rain will fall and the blackbody sheds it’s excess back to space.
I believe that is what is meant by ‘beyond the greenhouse’.
What is missing is the ratio of extra heat input vs how much the blackbody actually warms.
You might have 7 w/m^2 in, and only retain 1 w/m^2 as a higher equilibrium.

Harold Pierce Jr says:
September 15, 2010 at 4:02 am ,
It gets even more interesting to me. While averages aren’t the end-all in solutions, sometimes they tell the tale. I ran the numbers on a 1 dimensional model by increasing h2o content according to absolute humidity increase if one holds relative humidity constant. A 5 deg C rise assumption in the atmospheric column resulted in a mere 30% increase in the amount of water vapor. Remember that one must talk doublings (100%) for significant changes in the IR radiation effects. A 30% increase of h2o has a slightly lower effect than a doubling of co2 – thought to be around 3.7w/m^2. Combined, they provide less than 40% of the forcing required for a 5 deg C rise – enough for almost a 2 deg C rise, since co2 by itself is expected to be able to increase temperatures by around 1 deg C. Going with 2 deg C, the absolute humidity increase for a constant RH (assumption accepted by many climatologists as being true on average) is closer to 13% and drops down to under half the w/m^2 effect of the co2 – leaving us with a need to have more forcing to achieve 2 deg C rise for the co2 doubling and h2o vapor increase.
Apparently now that added forcing is supposed to occur by having fewer clouds along with the increase in water vapor. That too has a problem in that clouds provide both positive and negative effects with the negative effects outweighing the positive by a small portion of the total.
Since it is claimed that the h2o vapor is the primary ‘feedback’ mechanism, it would seem that either the claim is falsified or the claim of high sensitivity is falsified.

“”” Bob_FJ says:
September 15, 2010 at 11:24 pm
Surely everyone has heard of evaporative cooling?
* Why is it said that a healthy dog has a cold (moist) nose?
* Why did the young Jacqueline Bisset become famous for her wet T shirt scenes in the movie “The Deep”, of 1997?
http://www.mademan.com/chickipedia/jacqueline-bisset/
SORRY, but to be more serious:
The K & T “Earth’s Energy Budget” diagram, (in some quarters referred to as the “Trenberth Cartoon), in the IPCC’s AR4 report of 2007, claims that by far the greatest proportion of energy leaving the Earth’s surface is via evapo-transpiration. (~46% of all the four basic processes).
So, if there is warming, particularly of the ocean surfaces, should there not be a nominal increase in evaporation? (cooling). Given that the greatest proportion of cooling is suggested to be evapo-transpiration? Surely a small increase in this would be significant.
Yes; I agree, it is complicated, but why is there not more attention paid to this basic point in Physics?
BTW, there is an elegantly simple explanation for evaporative cooling in quantum theory: Any fluid has a mix of molecules of varying energy levels. (speeds). Thus the hotter molecules are more able to escape and leave a higher proportion of lower energy (colder-slower) molecules behind. “”””
Well I wouldn’t exactly call it quantum theory; just ordinary classical statistical Mechanics. For an “ideal” gas there is the Maxwell-Boltzmann distribution of velocities; and in liquids you have a similar distribution; but as you say; the higher energy molecules are the ones that have a greater probability of escaping from the surface into the atmosphere; which leaves a lower average molecular energy behind which is thus a cooling of the surface.
But this is peanuts compared to the Latent heat of Evaporation that leaves the liquid upon evaporation. That energy really is the energy that is required to separate the moleculse so they can act independently of each other except for the occasional collisions; whereas in the liquid phase they are somewhat bound to each other by attractive forces.
In the ideal gas the RMS velocity of the molecules is proportional to the square root of the Temperature (Kelvins); and this velocity distribution is part of the reason for a Doppler broadening of the spectral absorption lines with Temperature; although it is a fairly small effect at atmospehric Temperatures.

Geoge E Smith
Sept 16, 7:10pm
George, I find the arguments along that line to be rather effect at getting warmistas to quickly change the subject to avoid it.
The latent heat absorbed from evaporation carries far more energy than a few degrees of additional temperature and it is carried aloft by lower density moist air where it is released as it must be given off for condensation high up in the air, above most of the water vapor lower down – which is the dominant ghg. The condensation forms into water droplets or ice, becoming radiators of a continuum rather than a spectrum at the cloud tops.
The supposed added energy in the system due to more co2 is mostly hitting the water surface and not penetrating any distance below the surface skin like visible light is only going to raise the energy of the surface skin because all the heat flow mechanisms are working against it heating downward – at least for almost all the surface area. Ever try to boil a pot of water by heating the top? You’ve got a nice heating mechanism to provide the latent energy right where it is needed. Or should I say you’ve got a very nice mechanism to suck out the added IR and carry it out from the surface area. The formation of clouds and blocking of incoming sunlight will have even more of an effect to reduce warming. That leaves the warmistas with the problem of how to explain that more h2o vapor and a more active water vapor cycle will result in substantially less cloud formation that will allow more sunlight energy in.

“”” cba says:
September 17, 2010 at 4:48 am
Geoge E Smith
Sept 16, 7:10pm
George, I find the arguments along that line to be rather effect at getting warmistas to quickly change the subject to avoid it.
The latent heat absorbed from evaporation carries far more energy than a few degrees of additional temperature and it is carried aloft by lower density moist air where it is released as it must be given off for condensation high up in the air, above most of the water vapor lower down – which is the dominant ghg. The condensation forms into water droplets or ice, becoming radiators of a continuum rather than a spectrum at the cloud tops. “””
cba, it frustrates the hell out of me; that the evaporative cooling principle seems to go right over so many people’s heads.
I don’t keep a table of the heat capacity of water vapor in my head; but the way I fake it, is to remember that at the normal boiling point (100 deg C) the Latent heat of evaporation (at astp) is (or used to be) 539 cal/gm. If the temperature of evaporation is lower than that; say 30 deg C, then I simply add on one extra calorie for every degree below 100. I don’t know whether that is because of the Principle of cussedness, or what but it just seems to be the right thing to do, since that many calories is what it would take to get the 30 deg water to 1oo and then another 539 to boil it.
And that is just so much more energy than the question of the high velocity tail of the Maxwell-Boltzmann statistical spread issue that Gerry raised. His point is valid; it’s just not material because of the latent heat.
Then the other issue is that direct solar spectrum 6,000K BB spectrum energy from the sun, penetrates deeply (coupla hundred metres) into the ocean; so it doesn’t immediately inspire a whole lot of evaporation.
On the other hand the LWIR emitted by the atmosphere or clouds, that reaches the surface (ocean), is absorbed in the top 10 microns of the ocean surface. At > 2.0 microns wavelength the absorption coefficient of water is about 1000 cm^-1, so the 1/e attenuation depth is 10 microns; so ok 50 microns for 99% absorption. At 3.0 microns the coefficient goes to a wild 8,000 cm^-1, but beyond that it settles into the 1-2,000 range.
So whether that atmospheric radiation was due to CO2 or H2O or CH4 GHG heating; or whether it was caused by direct H2O vapor absorption of incoming solar energy in the 0.75-3 micrin range; that LWIR is the primary instyigator of surface evaporation. How many times have I read here, that the warmer atmosphere encourages more evaporation ? No it doesn’t; it is the warmer water that encourages evaporation; the H2O molecule doesn’t even know the atmosphere is there, warm or not, until it breaks free of the surface and eventually clobbers into some N2/O2/Ar critter.
Yes it is nice to have warmer air to hold more water; but the water is going to rise any way to where the air is colder; it is even nicer to have some wind to carry off that H2O before it gets a chance to return to the surface.
I’m not a chemist; but even I know that physical/chemical reaction rates can be limited by the ability to remove the reaction products from the reaction site. whether you are laying down epitaxial Gallium Arsenide or boiling water; you better deal with the effluent at the interface, if you want the reaction to continue.
That fundamental distinction between the “Forcing” due to solar spectrum energy hitting the water, and that due to LWIR thermal radiation doing the same thing, is fundamental to understanding those interractions.
Too many so-called climate scientists seem to think that one “forcing (w/m^2) ” is as good as another.
No! they behave quite differently.
And once that H2O escapes the surface; it just keeps on rising until it gets high enough and cold enough to revert to liquid/solid and relinquish that 609 cal per gr or even 689 if it becomes an ice crystal. And that energy is all transported to where ther is much less gHG interference with the thermal radiation that is generated at that altitude.
The evaporation/Convection thermal mechanisms are the biggest energy transporters (at these Temperatures); and that is why my computer CPU has a phase change convective heat pipe cooler. Eventually, Stefan-Boltzmann wins the game at higher Temperatures; but in the atmosphere it is the swamp cooler mechanism that works best.

ALL: Correction to my September 15, 2010 at 11:24 pm
The movie “The Deep”, which demonstrates one effect of evaporative cooling, was released in 1977, not 1997
George E. Smith Reur September 16, 2010 at 7:10 pm
I do not see evaporative cooling as a separate process to latent heat loss. In the case of evaporation of water, this phase change from liquid to vapour (gas) is very slow, (compared to that of vapourisation of boiling point), but my quick Google around gave the energy involved for evaporation at ~600 calories/gram. This is a measure of the cooling effect which also involves a change in temperature, as distinct from as in the boiling of water.
Well I [George] wouldn’t exactly call it quantum theory; just ordinary classical statistical Mechanics.
Perhaps I should have described the process as “Quantum Mechanics” instead of “Quantum Theory”, since the theory of escaping higher energy molecules is so well demonstrated. (Has it actually been observed?)

I tried posting the following over at Roy Spencer’s blog, but it has been stuck in modertion for three days. (it seems that the spam filter did not like the links)
Christopher Game, thanks your reply of September 22, 2010 at 12:26 PM , Concerning the potential feedback resulting from evapotranspiration. (E-T)
The IPCC has estimated in 4AR that the forcing for anthro’ CO2 is about 1.7 W/m^2, and that the net for all anthropogenic forcings is about the same value.
http://en.wikipedia.org/wiki/File:Radiative-forcings.svg
Adding to my earlier comment, according to Trenberth, 2007 levels of E-T resulted in a forcing of -78 W/m^2. Thus, without disputing his numbers, if (E-T) were to increase by say 1% in order to achieve some arbitrary increased water vapour level, there would be a feedback of -0.78 W/m^2, which is rather significant by comparison.
Dare I add that Trenberth also gives “Thermals” as another -24 W/m^2, and that I think that there should also be an increase in thermals too.
Add clouds, and how now to 2xCO2 sensitivity, I would think.
If you need it, the Trenberth chart is here:
http://www.flickr.com/photos/26175880@N05/3065365160/
What do you think?